Sitting around the table in the Whitehall crisis room, Margaret Thatcher and
her most senior ministers listened to the grim news coming in as World War
Three unfolded.

A Royal Navy aircraft carrier had been attacked, chemical weapons had been used on British forces and it would be only a matter of days before either Nato or the enemy launched atomic missiles.

Fortunately, the meetings held in the Cobra emergency briefing room in the first week of March 1983 were all part of a highly sophisticated real-time “war game”, and the feared nuclear conflict with the Soviet Union never transpired.

But senior civil servants who played the roles of Mrs Thatcher and members of her Cabinet in the exercise have spoken of the deadly seriousness with which they took the simulation, which could easily have been for real.

Sir David Goodall, then deputy secretary of the Cabinet Office, stood in for the prime minister at this and several other war games carried out in Whitehall during the latter years of the Cold War.

On one occasion he had the unsettling experience of pretending to be Mrs Thatcher while she was in the room. He recalled: “We were sitting around the table. We personified a war cabinet and various hypothetical events were then presented to us, and we had to decide how ministers would have responded to them, in particular the prime minister.

“I do remember one exercise about nuclear deterrents. The prime minister came and watched it. I had the rather strange experience of impersonating the prime minister in her presence.”

Sir David said the biennial Nato-led war games, known as the Warning and Intelligence Exercise and Civil-Military Exercise, or Wintex-Cimex, were valuable for ensuring that Britain had a “credible” nuclear deterrent.

He recalled a discussion with Mrs Thatcher in which she said she was “sceptical” that the UK could ever actually use its atomic weapons.

Sir David said: “The problem with that is you don’t have any conviction because everybody knows you have got it and would never use it.

“These exercises led to discussion of what one’s strategy and tactics would actually be in the event of an East-West confrontation.”

The 1983 Wintex-Cimex exercise included a speech written by civil servants imagining how the Queen might address the nation on the outbreak of nuclear war.

Sir David said those taking part did not take great notice of the Queen’s speech.

“It was simply background colour to lend verisimilitude to it. It was just part of the background,” he added.

Another participant in the exercise, who did not want to be named, suggested that the Queen’s private secretary would probably have known that the war game was taking place, and may also have been told about her imagined broadcast to the nation.

“It is conceivable that in terms of working up the background, someone in Whitehall might have mentioned to the private secretary at the palace that this was being done, but I have no way to judge whether that was likely," he said.

The Wintex-Cimex simulation ended on March 9 1983 after Britain announced it was about to use its nuclear weapons against enemy military targets.

Diplomat Sir John Weston, who stood in for foreign secretary Francis Pym in 1983 and played the prime minister in later war games, said: "This was of course a 'command post exercise' only, but with a serious purpose.

“We were all very conscious that the credibility of Nato's deterrent strategy required the detailed planning to be kept regularly up to date, along with the associated professional expertise and management procedures, both in London and in other Nato capitals, as well as at Nato headquarters."

Decades later, Sir John published a poem called ‘Payload’ reflecting on his experience around the Cobra table, in which he wrote: “You need to have acted Prime Minister/in the Whitehall bunker, he told me once,/to know how it felt when our double agent/suddenly warned us the other side/took our latest nuclear play for real,/and had moved to First Strike Alert.”

Professor Peter Hennessy, a historian who has written widely about the inner workings of Whitehall, said the Wintex-Cimex war games were “very gripping”.

He added: “They are written as a collective Whitehall thriller. It’s essentially a novel.

“I’ve never seen a Queen’s speech before, but other ones have had speeches by the prime minister and home secretary. These things were written to add verisimilitude - in the middle of the 1968 one the Soviets land somebody on the moon ahead of the Americans.

“Everyone involved took it very seriously, and most of them have never forgotten it because you did peer into the abyss. The Russian intelligence service took immense pains to get this stuff.”